1. Field of the Invention
The present invention relates to a culture bag for culturing cells such as animal tissue. More particularly, it is concerned with a culture bag made of plastic sheet having good flexibility, clarity, and gas permeability.
2. Description of the Prior Art
The culture of cells (such as animal tissue) in opentype containers such as Petri dish and flask has a disadvantage that the culture medium is liable to contamination with airborne infectious microbes which enter the incubator when it is opened. To cope with this problem, there have been proposed a variety of closed-type containers as mentioned below.
"Biotechnology Series, Technique of Cell Culture" pp. 137-141, issued by Kodansha Scientific (1985), describes using plastic bags for the culture of wallsticking cells.
Japanese Patent Laid-Open No. 214178/1988 discloses a cell culture container consisting of a bag-like container proper (formed by bonding two flexible plastic sheets to each other) and an inlet tube and an outlet tube each provided with a coupler at its end. According to this disclosure, the container should be made of a different material depending on its use. For aerobic culture, the preferred material includes ethylene-vinyl acetate copolymer, polyethylene, polypropylene, polybutadiene, Teflon.RTM., and silicone rubber, which have good gas permeability. For anaerobic culture, the preferred material includes polyvinylidene chloride, polyvinyl alcohol, polyethylene terephthalate, and copolymer of acrylonitrile-butadiene rubber grafted with acrylonitrile and methyl methacrylate, which have good gas barrier properties. In addition, these materials may be combined with one another to form a laminate, if necessary.
Japanese Patent Laid-open No. 202378/1988 (U.S. patent Ser. No. 008,213) discloses a technique of culturing specific cells in an airtight container provided with an access tube. According to this disclosure, the airtight container is made of a copolymer film about 0.04-0.23 mm thick, having an oxygen permeability not smaller than about 1.8.times.10.sup.5 .mu.m.sup.3 (STP) per m.sup.2.sec.Pa. The copolymer film is one which is formed by lamination or coextrusion from any of (a) ethylene-.alpha.-olefin (C.sub.4-10) copolymer having a density of about 0.91-0.925 g/cm.sup.3, (b) ethylene-methacrylic acid copolymer, (c) an ionomer, and (d) ionomer/polyester elastomer and linear low-density polyethylene elastomer.
The containers proposed in the above-mentioned disclosures have a disadvantage in clarity and gas permeability and hence they cannot be used as cell culture bags.
Japanese Patent Publication No. 50063/1980 (U.S. Pat. No 3,780,140) discloses a resin composition from which to produce flexible plastic containers. This resin composition is composed of a copolymer consisting essentially of (a) 40-80 wt. % ethylene, (b) 3-30 wt. % carbon monoxide, and (c) 5-60 wt. % comonomer (preferably vinyl acetate) and polyvinyl chloride or any other polymer in an amount low enough for it to be compatible with said copolymer.